The invention relates to a method for controlling the steering angle of at least one steered wheel of a vehicle and a system to carry out the method.
From the DE 197 02 313 C1 a method is known for controlling the steering angle of a vehicle, which has as its subject the so-called steering-by-wire. Here, the steering member, usually the vehicle steering wheel, is not coupled with the steered wheels of the vehicle in a mechanically rigid manner. Rather, a control unit is intercalated which, dependent on the signal which originates from the control member, actuates specific adjustment drives which alter the steering angle. The extent of the alteration to the steering angle can also be dependent here on the speed of the vehicle, i.e. the same steering turn on the steering member leads to different steering angles or changes to steering angles at different speeds, so that a vehicle travelling quickly reacts relatively slowly to steering turns. This has the following disadvantage: if an obstacle which appears abruptly has to suddenly be evaded, e.g. an animal jumping onto the roadway, the vehicle reacts too slowly to the abrupt, great steering locks.
The invention provides a method for controlling the steering angle of a vehicle and a system suitable for carrying out the method, which offer a high degree of comfort at different vehicle speeds and a high degree of vehicle safety even in the case of obstacles which suddenly occur. The method proposed comprises the following steps:
providing an adjustment drive coupled with the steering wheel and able to amend the steering angle,
providing a steering member to be actuated by a driver to steer the vehicle,
providing a control unit which is coupled with the steering member and the adjustment drive,
providing a distance meter coupled with the control unit to detect an obstacle for the vehicle,
the control unit controlling the adjustment drive to alter the steering angle, upon an alteration to a position of the steering member,
the extent of the alteration to the steering angle being dependent on whether an obstacle for the vehicle is detected or not by means of the distance meter.
The method proposed makes provision that with a suddenly occurring obstacle, despite of a high speed for example, an alteration to the steering angle is possible, which is substantially greater than the alteration to the steering angle when travelling normally, i.e. without an obstacle. By means of the method, therefore, in extreme situations a more immediate steering of the vehicle can be achieved. Thereby it is possible in extreme situations to still evade an obstacle, which would not be possible with the methods conceived hitherto.
According to a development of the invention, the quantitative alteration to the steering angle (i.e. the extent of the steering angle alteration associated with a defined alteration to the position of the steering member) is dependent on the period of time after which the vehicle would strike against the obstacle. In concrete terms, this means that with the same steering turn of the steering member, the control unit provides for different steering angles on the wheels themselves, depending on how close in terms of time a collision with the obstacle is imminent. Therefore, the risk of a collision is to be determined and is to flow into the steering angle. With the same turn of the steering member, the control unit would provide for a smaller steering angle when the collision with the obstacle is still one second ahead than in the case in which the collision is only a few tenths of a second ahead, for example.
A further possibility for determining the likelihood of the collision with the obstacle consists in making the quantitative alteration to the steering angle dependent on the relative speed between the vehicle and the obstacle.
According to the preferred embodiment, the control unit also alters the steering angle quantitatively as a function of the speed of the vehicle. This means, as already previously explained, that the same steering turn on the steering member at higher speeds provides for a substantially smaller steering angle alteration than at low speeds. The extremes are, for example, high speed on motorways and low speeds, but high steering angle alterations, e.g. when parking the vehicle. Through the dependence on speed, provision is made that when parking great alterations to the steering angle are possible with relatively small steering turns and the vehicle does not act in a nervous manner at maximum speed, reacting to small steering locks.
A further development of the invention makes provision that a so-called ESP system (electronic stabilizing program) is integrated into the control unit. Thereby, the alteration to the steering angle is also dependent on the ambient conditions of the vehicle (in particular the friction value between wheels and roadway), whereby it is to be prevented that the steering turn angles which are possible at high speeds lead to skidding of the vehicle.
The system according to the invention for controlling the steering angle of at least on steered wheel of the vehicle comprises an adjustment drive coupled with the steering wheel and able to amend the steering angle, a steering member to be actuated by a driver to steer the vehicle, a control unit coupled with the steering member and the adjustment drive, and a distance meter coupled with the control unit to detect an obstacle for the vehicle. The control unit controls the adjustment drive to alter the steering angle, upon an alteration to a position of the steering member. Further, the control unit is able to amend an extent of the alteration to the steering angle dependent on whether an obstacle for the vehicle is detected or not by means of the distance meter.
In addition, a distance meter, in particular a distance radar, is provided, which is coupled with the control unit and which detects obstacles.
Preferably the system is also equipped with a speed sensor which is coupled with the control unit, so that a steering is possible dependent on the speed of the vehicle.
Advantageously the steering member is coupled electrically with the control unit. Furthermore, in one embodiment the invention makes provision that an ESP control is integrated into the system.